1. Field of the Invention
This invention relates to improved methods for attaching a lid to a metal drum, particularly metal drums used for the storage and shipment of radioactive material. Typical drums of this type are the DOT 6M specification drums having a nominal volume of 55 gallons. The drums are stainless steel and conform to 49 CFR §178.504.
2. Background and Prior Art
Stainless steel drums of this type are used in the packaging for transport of radioactive materials and, frequently, for their storage. The drum is rolled steel, having a single welded seam and has a closed bottom end and an open top end. The open end of the drum has a rolled edge and the lid used to effect closure has a raised rim which partially surrounds the rolled edge of the drum. A gasket nominally seals the lid to the drum and a locking ring is pulled tight in the circumferential direction and typically held in place with a bolt passing through the lugs located on both ends of the gap in the locking ring. The arrangement is familiar to anyone who has handled standard 55-gallon open drums which are typically used in commerce for bulk shipping of solids and liquids.
Packages used for the transportation of radioactive materials are required to pass the Hypothetical Accidents Condition (HAC) 30-Ft. Drop Test. When used to ship fissile materials, the contents are enclosed within the drum using a “overpack” consisting of multiple layers of fiberboard discs about a central canister.
A limited number of closure systems are available for 55-gallon drums but can be simply described as those of the split-ring type which are bolted together and those which involve a lever which puts tension on the ring and is snapped into place using a hook attached to the ring. Some examples are found in U.S. Pat. No. 4,314,720 to Santoni which uses a locking lever; U.S. Pat. No. 4,957,317 to Jakubas which uses a shuttle wrench and bolt to make the drum tamperproof; U.S. Pat. No. 5,193,804 to Coleman which discloses a spring in the locking ring 180° from the bolt lugs; U.S. Pat. No. 5,971,190 to Manning which adds a pair of projections to the lugs to improve alignment; and, U.S. Pat. No. 6,435,576 B1 to Kusta, which adds a jam nut between lugs to improve alignment. Specification No. 1A2-102-00 describes United Nations designation UN 1A2 as a required packaging when an open head steel drum is used and requires a stainless steel locking ring, welded lugs, one lug threaded and a stainless steel bolt having a nominal minimum size of 0.625 inches. The closure is to conform to 49 CFR §178.2(c)(1). No options are specified.
Testing has shown that when a 55-gallon drum is packed to the maximum allowable weight of 640 pounds (weight of contents approximately 460 pounds) the integrity of the package is not guaranteed when dropped from 30 feet onto the open head at an angle which puts the center of gravity directly over the corner (CGOC test). In typical tests, the primary cause of failure appears to be deformation of the rim of the drum. The difficulties are addressed in Blanton, P. S. and A. C. Smith, “Response of Conventional Ring Closures of Drum Type Packages” WSRC-MS-2002-00452.
It is an object of this invention to provide a ring closure which does not fail the aforementioned test. It is a second objective of this invention to provide a means for strengthening the rim of the drum without changing the design and method of manufacture of the drum.
It is a third objective of this invention to provide a ring closure which can be applied quickly using the same tools and same skills as are required to use the existing ring closures.